Our aim is to undestand the mechanisms for the functions of the excitable membrane and cilia by using genetic dissection. This is done by producing molecular lesions with mutagenesis and analyzing the resultant effects on behavior, electrophysiology and the biochemical composition of the system. Paramecium was chosen as th model system because both genetics and physiology have been well advanced on this unicell. Over 200 lines of behavioral mutants, representing over 75 independent mutations, were isolated. Most of them were genetically verified as single nuclear genic mutants. "Pawns", for example are mutants which fail to generate the Ca-action potential and thus fail behaviorally to avoid various stimuli. These mutants most likely carry molecula defects in the voltage-sensitive Ca-gates on their membranes. "Fast-2", a mutant which fails to avoid Na ion appears to have an abnormally large permeability to K ion in the presence of Na ion. Other types of behavioralmutants have been shown to be either membrane or ciliary mutants. Biochemical studies are now in progress to search for the macromolecular gene products which relate to the vital functions of the membrane and cilia.